Wireless communication systems have been widely deployed in order to provide various types of communication services such as voice or data services. Generally, a wireless communication system is a multiple access system capable of supporting communication with multiple users by sharing available system resources (bandwidth, transmit power, etc.). Multiple access systems include, for example, a code division multiple access (CDMA) system, a frequency division multiple access (FDMA) system, a time division multiple access (TDMA) system, an orthogonal frequency division multiple access (OFDMA) system, and a single-carrier frequency division multiple access (SC-FDMA) system.
Standards for a wireless local area network (WLAN) technology have been developed by the institute of electrical and electronics engineers (IEEE) 802.11 group. IEEE 802.11a and b use an unlicensed band at 2.4. GHz or 5 GHz and IEEE 802.11b provides a transmission rate of 11 Mbps. IEEE 802.11a provides a transmission rate of 54 Mbps. IEEE 802.11g provides a transmission rate of 54 Mbps by applying orthogonal frequency division multiplexing (OFDM) at 2.4 GHz. IEEE 802.11n provides a transmission rate of 300 Mbps by applying multiple input multiple output (MIMO)-OFDM. IEEE 802.11n supports a channel bandwidth of up to 40 MHz and, in this case, provides a transmission rate of 600 Mbps. IEEE 802.11p is a standard for supporting wireless access in vehicular environments (WAVE). For example, 802.11p provides improvements necessary for support of intelligent transportation systems (ITS). IEEE 802.11ai is a standard for supporting fast initial link setup of an IEEE 802.11 station (STA).
With recent widespread application of a short-range communication technology, such as Wi-Fi, to the market, devices may be directly connected to each other instead of being connected to each other via a local network. One technology for a direct connection between devices using Wi-Fi is Wi-Fi Direct.
Wi-Fi Direct is a standard for network connectivity technologies that describes operation of a link layer. With the lack of definitions of regulations or standards for applications on top of Wi-Fi Direct, when applications are executed after a connection between Wi-Fi Direct devices is established, interoperability and inconsistency in operation between the devices occur. Due to these problems, a standard specification, called Wi-Fi Direct services (WFDS), including the technical contents of higher-layer applications is being developed by the Wi-Fi alliance (WFA).
As the WFA has recently announced a new specification for data transfer through a direct connection between mobile devices, called Wi-Fi Direct, accelerated technology development of relevant institutes is ongoing to meet a Wi-Fi Direct specification. In a strict sense, Wi-Fi Direct is a marketing term corresponding to a trademark and is referred to as Wi-Fi peer-to-peer (P2P) in a technical specification therefor. Accordingly, Wi-Fi Direct and Wi-Fi P2P are used interchangeably in the present invention in dealing with a Wi-Fi based P2P technology. In a traditional Wi-Fi network, generally, a Wi-Fi equipped device accesses an Internet network via an access point (AP). A data communication method through a direct connection between devices has been conventionally used by some users using devices such cellular phones or notebook PCs adopting a wireless communication technique such as Bluetooth. However, a transmission rate is low and an actually used transmission distance is limited to 10 m or less. Especially, when this method is used in an environment in which large-capacity data transmission is needed or many Bluetooth devices are present, there is a technical limitation in performance that a user feels.
Meanwhile, Wi-Fi P2P has added parts for supporting direct communication between devices while maintaining most functions of an existing Wi-Fi standard specification. Therefore, Wi-Fi P2P has an advantage of providing P2P communication between devices by sufficiently utilizing hardware and physical properties of Wi-Fi chip equipped devices and mainly upgrading software functions alone.
As is well known, Wi-Fi chip equipped devices have been expanded to various fields including notebook PCs, smartphones, smartTVs, game consoles, and cameras and have created a sufficient number of suppliers and technical development manpower. However, software for supporting the Wi-Fi P2P specification has not been actively developed. This is because relevant software capable of conveniently using the specification has not been distributed although the Wi-Fi P2P specification was announced.
A P2P group includes a device acting as an AP over an existing infrastructure network and this device is referred to as a P2P group owner (GO) in the P2P specification. There may be various P2P clients around the P2P GO. One P2P group includes only one GO and client devices corresponding to the other devices except for the GO.
FIG. 1 is a diagram illustrating a typical P2P network topology.
As illustrated in FIG. 1, a P2P GO may be directly connected to a client having a P2P function or may be connected to a legacy client having no P2P function.
FIG. 2 is a diagram illustrating a situation in which one P2P device forms a P2P group and simultaneously operates as an STA of a WLAN to be connected to an AP.
The P2P technical specification defines an operation mode of P2P devices as illustrated in FIG. 1 as a concurrent operation.
In order for a series of P2P devices to form a group, which of the device becomes a P2P GO is determined by GO intent values of a P2P attribute ID. These values range from 0 to 15. The P2P devices exchange the GO intent values and a device having the greatest value becomes the P2P GO. Meanwhile, although a legacy device that does not support Wi-Fi P2P technology may also belong to the P2P group, the function thereof is limited to accessing an infrastructure network through the P2P GO.
According to the Wi-Fi P2P specification, since the P2P GO transmits a beacon signal using OFDM, 11b specification is not supported and 11a/g/n specification may be used for Wi-Fi P2P devices.
To perform an operation for setting up a connection between a P2P GO and a P2P client, the P2P specification broadly includes the following four functions.
First, P2P Discovery deals with technical items such as device discovery, service discovery, group formation, and P2P invitation. For device discovery, two P2P devices exchange device related information such as device names or device types on the same channel. For service discovery, the P2P devices exchange information regarding a service to be used through P2P. Group formation is a function for forming a new group by determining which device becomes the P2P GO. P2P invitation is a function for calling a permanently formed P2P group or causing a P2P device to participate in an existing P2P group.
Second, P2P Group Operation describes formation and completion of a P2P group, connection to the P2P group, communication in the P2P group, a service for P2P client discovery, operation of a persistent P2P group, etc.
Third, P2P Power Management describes a P2P device power management method and a signal processing method at a power saving mode timing.
Last, Managed P2P device describes a method in which one P2P device forms a P2P group and simultaneously accesses an infrastructure network through a WLAN AP.
Characteristics of the P2P group will now be described. The P2P group is similar to an existing infrastructure basic service set (BSS) in that a P2P GO serves as an AP and a P2P client serves as an STA. Accordingly, a P2P device needs to be equipped with software capable of performing roles of the GO and the client. P2P devices are distinguished from each other using P2P addresses such as medium access control (MAC) addresses. Notably, P2P devices that perform communication in the P2P group using P2P interface addresses need not use globally unique ID addresses. The P2P group has a single P2P group ID comprised of a combination of a service set identifier (SSID) and a P2P device address of the P2P GO. In the Wi-Fi P2P specification, WPA2-PSK/AES is used for security. The life cycle of the P2P group includes a temporary connection method, and a persistent connection method in which the same connection is attempted after a predetermined time. In the persistent group connection method, once the P2P group is formed, roles, certification, SSIDs, and a P2P group ID of the devices are cashed and so that a quick group reconnection may be established by applying the same connection format.
A Wi-Fi P2P connection method will now be described. A Wi-Fi device connection process broadly includes two phases. The first phase is discovery in which two P2P devices find each other and the second phase is group formation in which the role of a P2P GO or a P2P client is determined between the discovered devices. The first discovery phase causes P2P devices to be connected to each other and includes a search state and a listen state. In the search state, the devices perform active search using a Probe Request frame. For quick search, the range of search is restricted and search is performed using social channels ch1, ch6, and ch11. A P2P device of the listen state maintains the listen state by selecting only one of the three social channels. Upon receiving the Probe Request frame transmitted by another P2P device in the search state, the P2P device responds with a Probe Response frame. The P2P devices may reach a common channel after repeatedly performing the search state and the listen state. For selective association after finding each other, the P2P devices use the Probe Request frame and the Probe Response frame to discover a device type, a manufacturer, or a familiar device name. In order to confirm whether an inter-device compatible service is present in the P2P group, the P2P devices may use service discovery. This is intended to determine whether a service provided in each device is compatible with another device. In the P2P specification, a specific service discovery specification is not designated. A user of the P2P device may search proximate P2P devices and services provided by the devices, thereby quickly connecting to a desired device or service.
Group formation, which is the second phase, will now be described. If the P2P devices complete the above-described discovery (find) phase, checking as to whether the counterpart device is present is completed. Based on the discovery phase, the two P2P devices need to enter a GO negotiation phase to configure a BSS. The negotiation phase is broadly divided into two sub-phases: a GO negotiation phase and a Wi-Fi protected setup (WPS) phase. In the GO negotiation phase, the devices negotiates with each other about a role as a P2P GO or a P2P client and set an operating channel to be used in the P2P group. In the WPS phase, typical operation is performed as in existing WPS, for example, exchange of PIN information input by a user on a keypad or simple setup through a push button. In the P2P group, the P2P GO is in charge of a core role of the P2P group. The P2P GO assigns a P2P interface address, selects an operating channel of the group, and sends a beacon signal including various operating parameters of the group. In the P2P group, only the P2P GO is capable of transmitting the beacon signal. Using the beacon signal, the P2P device quickly confirms the P2P GO and participates in the group in a scan phase which is an initial connection phase. Alternatively, the P2P GO may autonomously initiate a P2P group session or may initiate the session after using the method described in the P2P discovery phase. Since a value for the P2P GO performing an important role is not fixed for any device but is variable by an application or a higher-layer service, a developer may select a proper value corresponding to the P2P GO according to usage of an application program.
Next, P2P addressing will be described. A P2P device assigns a P2P interface address using a MAC address in a P2P group session. The P2P interface address of a P2P GO is a BSS ID which substantially indicates a MAC address of the P2P GO.
Disassociation of the P2P group will now be described. If a P2P session is ended, the P2P GO needs to inform all P2P clients that the P2P group session is ended through de-authentication. The P2P client may also perform disassociation for the P2P GO and, in this case, a disassociation procedure is needed if possible. Upon receiving a disassociation release request from a P2P client, the P2P GO may recognize that the P2P client has been disassociated. Upon sensing an abnormal protocol error from a P2P client or sensing a P2P client that hinders a connection of the P2P group from the P2P client, the P2P GO triggers rejection of authentication or denial of association. The P2P GO records the reason of failure in an association response and then transmits the response.
In a session connection procedure among the above processes, when a seeker device (service seeker) desires to use specific WFDS according to a conventional scheme, if an advertiser device (service advertiser) is configured not to permit automatic acceptance (auto_accept), the advertiser device may defer a session request but does not transmit information indicating that a session has been deferred to the seeker device. Accordingly, the seeker device has to wait until the session request for the deferred session is received again from the advertiser device. In addition, upon accepting the session request, a user of the advertiser device can determine only whether to accept the session request. Consequently, a procedure of transmitting additional information about the session request between two devices is needed.
These problems will now be described by way of example. It is assumed that the seeker device is a smartphone, the advertiser device is a printer device, and a service that the seeker device is to use is a print service for printing an image in the interior of the smartphone through the printer device. Although the printer device may be present in the vicinity of a smartphone user, the printer device may be installed in a place which is not near the smartphone user. In this case, the printer device may be configured to perform the print service only when the printer device accepts a service request. This is because the printer device may be configured not to permit auto_accept by the user although the printer device may immediately perform the print service with respect to a service request of the smartphone in the case in which the printer device is configured to permit anto_accept.
Accordingly, it is necessary to display information indicating that a session request for the print service has been deferred on the smartphone. Information about a session requested service may be displayed on the printer device so that additional information (e.g. information indicating that a print service is $0.1 per sheet) may be displayed for the user of the printer device.
In the case of the first session request between the smartphone and the printer device, information indicating that a session has been deferred may be included in a response message to the session request and then may be transmitted. However, if the smartphone and the print device have already been connected, there is no method for transmitting a message indicating that the session has been deferred.